lib/dnspython/dns/tsig.py

   1 # Copyright (C) 2001-2007, 2009, 2010 Nominum, Inc.
   2 #
   3 # Permission to use, copy, modify, and distribute this software and its
   4 # documentation for any purpose with or without fee is hereby granted,
   5 # provided that the above copyright notice and this permission notice
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   9 # WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
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  13 # ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT
  14 # OF OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
  15
  16 """DNS TSIG support."""
  17
  18 import hmac
  19 import struct
  20
  21 import dns.exception
  22 import dns.rdataclass
  23 import dns.name
  24
  25 class BadTime(dns.exception.DNSException):
  26     """Raised if the current time is not within the TSIG's validity time."""
  27     pass
  28
  29 class BadSignature(dns.exception.DNSException):
  30     """Raised if the TSIG signature fails to verify."""
  31     pass
  32
  33 class PeerError(dns.exception.DNSException):
  34     """Base class for all TSIG errors generated by the remote peer"""
  35     pass
  36
  37 class PeerBadKey(PeerError):
  38     """Raised if the peer didn't know the key we used"""
  39     pass
  40
  41 class PeerBadSignature(PeerError):
  42     """Raised if the peer didn't like the signature we sent"""
  43     pass
  44
  45 class PeerBadTime(PeerError):
  46     """Raised if the peer didn't like the time we sent"""
  47     pass
  48
  49 class PeerBadTruncation(PeerError):
  50     """Raised if the peer didn't like amount of truncation in the TSIG we sent"""
  51     pass
  52
  53 default_algorithm = "HMAC-MD5.SIG-ALG.REG.INT"
  54
  55 BADSIG = 16
  56 BADKEY = 17
  57 BADTIME = 18
  58 BADTRUNC = 22
  59
  60 def sign(wire, keyname, secret, time, fudge, original_id, error,
  61          other_data, request_mac, ctx=None, multi=False, first=True,
  62          algorithm=default_algorithm):
  63     """Return a (tsig_rdata, mac, ctx) tuple containing the HMAC TSIG rdata
  64     for the input parameters, the HMAC MAC calculated by applying the
  65     TSIG signature algorithm, and the TSIG digest context.
  66     @rtype: (string, string, hmac.HMAC object)
  67     @raises ValueError: I{other_data} is too long
  68     @raises NotImplementedError: I{algorithm} is not supported
  69     """
  70
  71     (algorithm_name, digestmod) = get_algorithm(algorithm)
  72     if first:
  73         ctx = hmac.new(secret, digestmod=digestmod)
  74         ml = len(request_mac)
  75         if ml > 0:
  76             ctx.update(struct.pack('!H', ml))
  77             ctx.update(request_mac)
  78     id = struct.pack('!H', original_id)
  79     ctx.update(id)
  80     ctx.update(wire[2:])
  81     if first:
  82         ctx.update(keyname.to_digestable())
  83         ctx.update(struct.pack('!H', dns.rdataclass.ANY))
  84         ctx.update(struct.pack('!I', 0))
  85     long_time = time + 0L
  86     upper_time = (long_time >> 32) & 0xffffL
  87     lower_time = long_time & 0xffffffffL
  88     time_mac = struct.pack('!HIH', upper_time, lower_time, fudge)
  89     pre_mac = algorithm_name + time_mac
  90     ol = len(other_data)
  91     if ol > 65535:
  92         raise ValueError('TSIG Other Data is > 65535 bytes')
  93     post_mac = struct.pack('!HH', error, ol) + other_data
  94     if first:
  95         ctx.update(pre_mac)
  96         ctx.update(post_mac)
  97     else:
  98         ctx.update(time_mac)
  99     mac = ctx.digest()
 100     mpack = struct.pack('!H', len(mac))
 101     tsig_rdata = pre_mac + mpack + mac + id + post_mac
 102     if multi:
 103         ctx = hmac.new(secret)
 104         ml = len(mac)
 105         ctx.update(struct.pack('!H', ml))
 106         ctx.update(mac)
 107     else:
 108         ctx = None
 109     return (tsig_rdata, mac, ctx)
 110
 111 def hmac_md5(wire, keyname, secret, time, fudge, original_id, error,
 112              other_data, request_mac, ctx=None, multi=False, first=True,
 113              algorithm=default_algorithm):
 114     return sign(wire, keyname, secret, time, fudge, original_id, error,
 115                 other_data, request_mac, ctx, multi, first, algorithm)
 116
 117 def validate(wire, keyname, secret, now, request_mac, tsig_start, tsig_rdata,
 118              tsig_rdlen, ctx=None, multi=False, first=True):
 119     """Validate the specified TSIG rdata against the other input parameters.
 120
 121     @raises FormError: The TSIG is badly formed.
 122     @raises BadTime: There is too much time skew between the client and the
 123     server.
 124     @raises BadSignature: The TSIG signature did not validate
 125     @rtype: hmac.HMAC object"""
 126
 127     (adcount,) = struct.unpack("!H", wire[10:12])
 128     if adcount == 0:
 129         raise dns.exception.FormError
 130     adcount -= 1
 131     new_wire = wire[0:10] + struct.pack("!H", adcount) + wire[12:tsig_start]
 132     current = tsig_rdata
 133     (aname, used) = dns.name.from_wire(wire, current)
 134     current = current + used
 135     (upper_time, lower_time, fudge, mac_size) = \
 136                  struct.unpack("!HIHH", wire[current:current + 10])
 137     time = ((upper_time + 0L) << 32) + (lower_time + 0L)
 138     current += 10
 139     mac = wire[current:current + mac_size]
 140     current += mac_size
 141     (original_id, error, other_size) = \
 142                   struct.unpack("!HHH", wire[current:current + 6])
 143     current += 6
 144     other_data = wire[current:current + other_size]
 145     current += other_size
 146     if current != tsig_rdata + tsig_rdlen:
 147         raise dns.exception.FormError
 148     if error != 0:
 149         if error == BADSIG:
 150             raise PeerBadSignature
 151         elif error == BADKEY:
 152             raise PeerBadKey
 153         elif error == BADTIME:
 154             raise PeerBadTime
 155         elif error == BADTRUNC:
 156             raise PeerBadTruncation
 157         else:
 158             raise PeerError('unknown TSIG error code %d' % error)
 159     time_low = time - fudge
 160     time_high = time + fudge
 161     if now < time_low or now > time_high:
 162         raise BadTime
 163     (junk, our_mac, ctx) = sign(new_wire, keyname, secret, time, fudge,
 164                                 original_id, error, other_data,
 165                                 request_mac, ctx, multi, first, aname)
 166     if (our_mac != mac):
 167         raise BadSignature
 168     return ctx
 169
 170 def get_algorithm(algorithm):
 171     """Returns the wire format string and the hash module to use for the
 172     specified TSIG algorithm
 173
 174     @rtype: (string, hash constructor)
 175     @raises NotImplementedError: I{algorithm} is not supported
 176     """
 177
 178     hashes = {}
 179     try:
 180         import hashlib
 181         hashes[dns.name.from_text('hmac-sha224')] = hashlib.sha224
 182         hashes[dns.name.from_text('hmac-sha256')] = hashlib.sha256
 183         hashes[dns.name.from_text('hmac-sha384')] = hashlib.sha384
 184         hashes[dns.name.from_text('hmac-sha512')] = hashlib.sha512
 185         hashes[dns.name.from_text('hmac-sha1')] = hashlib.sha1
 186         hashes[dns.name.from_text('HMAC-MD5.SIG-ALG.REG.INT')] = hashlib.md5
 187
 188         import sys
 189         if sys.hexversion < 0x02050000:
 190             # hashlib doesn't conform to PEP 247: API for
 191             # Cryptographic Hash Functions, which hmac before python
 192             # 2.5 requires, so add the necessary items.
 193             class HashlibWrapper:
 194                 def __init__(self, basehash):
 195                     self.basehash = basehash
 196                     self.digest_size = self.basehash().digest_size
 197
 198                 def new(self, *args, **kwargs):
 199                     return self.basehash(*args, **kwargs)
 200
 201             for name in hashes:
 202                 hashes[name] = HashlibWrapper(hashes[name])
 203
 204     except ImportError:
 205         import md5, sha
 206         hashes[dns.name.from_text('HMAC-MD5.SIG-ALG.REG.INT')] =  md5.md5
 207         hashes[dns.name.from_text('hmac-sha1')] = sha.sha
 208
 209     if isinstance(algorithm, (str, unicode)):
 210         algorithm = dns.name.from_text(algorithm)
 211
 212     if algorithm in hashes:
 213         return (algorithm.to_digestable(), hashes[algorithm])
 214
 215     raise NotImplementedError("TSIG algorithm " + str(algorithm) +
 216                               " is not supported")